This invention relates to packaging apparatus, and more particularly to apparatus for wrapping products in heat-shrinkable film for subsequent shrinking in a shrink tunnel.
The invention is especially concerned with apparatus of a type heretofore sold by the assignee of this application known as a "sleeve wrapper," in which a unit to be wrapped is fed forward by a conveyor against a vertical reach of film comprising a first web issuing from an upper roll and extending downwardly and a second web issuing from a lower roll and extending upwardly with the ends of the two webs heat-sealed together. As the unit moves forward, the upper web is draped over the unit and the lower web is draped under it. The unit then dwells in place while a pair of seal bars are closed behind the unit to heat-seal the two webs together on the trailing side of the unit and to sever the webs through the seal so as to provide a trailing seal for the film draped around the unit to form a sleeve, and a seal constituting the leading seal for the next sealing operation. After the sealing operation, the bars are opened and the enwrapped unit is fed forward away from the webs and another unit fed forward for being wrapped.
In the assignee's prior sleeve wrapping apparatus, the conveyor (and seal bars) have been intermittently operated in sealing cycles via start-and-stop electric motor operation under control of a photoelectric cell and this has tended to cause problems when attempting to wrap units of low stability, at commercially necessary speeds, the acceleration and deceleration characteristics of this type of operation being such as to tend to cause units of low stability to tip over and/or to become disoriented on starting and stopping the conveyor.